Gravitational Collapse of Magnetized Clouds. I. Ideal Magnetohydrodynamic Accretion Flow

By Daniele Galli, S. Lizano, F. Shu, A. Allen. 2006

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We study the self-similar collapse of an isothermal magnetized rotating cloud in the ideal magnetohydrodynamic (MHD) regime. In the limit of small distance from the accreting protostar, we find an analytic solution that corresponds to free fall onto a central mass point. The density distribution is not spherically symmetric but depends on the mass loading of magnetic field lines, which can be obtained by matching our inner solution to an outer collapse solution previously computed by Allen et al. The concentration of magnetic field trapped by the central mass point under field freezing, independent on the details of the starting state, creates a split-monopole configuration in which the magnetic field strength increases as the inverse square of the distance from the center. Under such conditions, the inflow eventually becomes sub-Alfvènic and the outward transfer of angular momentum by magnetic braking very efficient, thus preventing the formation of a centrifugally supported disk. Instead, the azimuthal velocity of the infalling gas decreases to zero at the center, and the gas spirals into the star. Therefore, the dissipation of dynamically important levels of magnetic field is a fundamental requisite for the formation of protoplanetary disks around young stars.

Subfields: Astronomy and Astrophysics, Instrumentation, Statistical and Nonlinear Physics

View Paper: https://www.semanticscholar.org/paper/9840bf08381a7d9fb4d86c27236f55d48f079df3

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Citations in the corpus

On the diversity and statistical properties of protostellar discs (2018, background): “…the axis of rotation of a core is aligned with a global field that is anchored at large distances from the centre of the core (Allen et al. 2003; Galli et al. 2006; Price & Bate 2007; Mellon & Li 2008; Hennebelle & Fromang 2008; Duffin & Pudritz 2009; Dapp & Basu 2010; Machida et al. 2011; Li…”
A millimeter Continuum Size–Luminosity Relationship for Protoplanetary Disks (2017, background): “Disk sizes reflect some convolution of the processes involved in formation (Galli et al. 2006; Mellon & Li 2008; Vorobyov 2009; Dapp & Basu 2010; Machida et al. 2011), evolution of angular momentum (e.g., Lynden-Bell & Pringle 1974; Hartmann et al. 1998), and, perhaps most importantly, the growth…”
NON-IDEAL MHD EFFECTS AND MAGNETIC BRAKING CATASTROPHE IN PROTOSTELLAR DISK FORMATION (2011, background): “…is that, in the ideal MHD limit, flux freezing allows the infalling material to drag a finite amount of magnetic flux into the central object, creating a split magnetic monopole whose (poloidal) field strength increases rapidly with decreasing radius (as r−2, Galli et al. 2006; see their Fig.”
Magnetic Braking and Protostellar Disk Formation: The Ideal MHD Limit (2007, background): “The braking is greatly enhanced by the equatorial pinching of field lines, which lengthens the magnetic lever arms (ALS03, Galli et al. 2006).”
Protostellar disk formation and transport of angular momentum during magnetized core collapse (2012, result): “Similar conclusions were reached by Galli et al. (2006), who performed analytical studies of magnetized collapsing cores.”
Collapse, outflows and fragmentation of massive, turbulent and magnetized prestellar barotropic cores (2011, result): “This is at variance with the conclusion that even low values of the magnetic field could entirely suppress the formation of a disk, as previously inferred by Allen et al. (2003), Galli et al. (2006), Price & Bate (2007), Hennebelle & Fromang (2008), and Mellon & Li (2008, 2009).”
Theory of Star Formation (2007, background): “Indeed, magnetic braking when the field is frozen to the matter is so effective that Allen, Li, & Shu (2003) and Galli et al. (2006) have argued that magnetic reconnection is required to reduce the field and therefore the braking enough that a Keplerian disk can form.”
Ambipolar diffusion in low-mass star formation - I. General comparison with the ideal magnetohydrodynamic case (2015, background): “…as a result of the very effective magnetic braking created by a strong pile-up of magnetic flux towards the centre of the collapsing system (Galli et al. 2006, Allen et al. 2003, Price & Bate 2007; Hennebelle & Teyssier 2008; Matsumoto & Tomisaka 2004; Hennebelle & Fromang 2008; Commerçon…”
ANALYTICAL THEORY FOR THE INITIAL MASS FUNCTION. II. PROPERTIES OF THE FLOW (2009, background): “…magnetic field, which has been shown to severely inhibit disk fragmentation (Machida et al. 2005, 2008, Hennebelle & Teyssier 2008, Price & Bate 2008) or even to prevent disk formation by magnetic braking (Galli et al. 2006, Price & Bate 2007, Hennebelle & Fromang 2008, Mellon & Li 2008a,b).”
Disk formation during collapse of magnetized protostellar cores (2009, background): “Indeed various studies have already demonstrated that internal magnetic braking is more complex (e.g.; Galli et al. 2006, HF08).”